Naked mole-rats (Heterocephalus glaber) have long-fascinated scientists. As well as living to be 30 years old or more, they are one of only two eusocial mammal species. This means that, like honeybees and other eusocial insects, they live in large colonies of up to 300 individuals that collectively raise their relatives born to one queen – a single breeding female. Queens aggressively intimidate their subordinates to keep them from reproducing, and if a queen dies, another female mole-rat will take over.

With such long lives, studying ageing in naked mole-rats takes time, and much previous work has only used a few individuals over a short timescale. But this new study uses a population of naked mole-rats for which the first individuals were collected in 1980. Scientists at the ageing research company Calico in the US used data from more than 3000 individuals recorded over 35 years to look at the whole lifespan of the rodents.

The law that determines the rate of death in humans is known as the Gompertz-Makeham law of mortality. According to this law, the rate of death increases exponentially with age – the older a person is, the more likely they are to die. This is also true of other animals studied, including horses and mice.

But naked mole-rats defy this law. The researchers found little or no signs of ageing in the rodents, regardless of their sex or whether or not they had reproduced. This sets them apart from all other mammals previously studied.

Rochelle Buffenstein, one of the study’s authors, said that the mole-rats’ lifespan is much longer than would be expected from their small size. “Our research demonstrates that naked mole rats do not age in the same manner as other mammals,” she said, “and their risk of death does not increase even at 25 times past their time to reproductive maturity.”

Calico, which is owned by Google’s parent company, Alphabet, hopes to use knowledge gained from studies like this one to advance work on human ageing.

“These findings,” Buffenstein says, “reinforce our belief that naked mole rats are exceptional animals to study to further our understanding of the biological mechanisms of longevity.”